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Are Chow Chows at Greater Risk of Death During

Anesthesia and Surgery Than Other Dogs?

Carmen Jane Booth, D.V.M., Ph.D.
Redfire Chow Chows

As a member of the Chow Chow Club Incorporated, the patient has the severe rise in body temperature. In an
Health Committee, unanticipated deaths in Chow updated review from the same researchers, they report
Chows is a serious concern. It is hard enough when one the prevalence of the genetic abnormalities may be as
of our beloved Chows passes at an advanced age after a great as one in 400 individuals. MH affects humans, cer-
long wonderful life, but to have a young dog die follow- tain pig breeds, dogs and horses. The earliest diagnostic
ing routine, elective, non-emergency surgery is devastat- clue is an increase in carbon dioxide production by mea-
ing for not only the owner, but also veterinarians and surement of end-tidal carbon dioxide production despite
clinic staff involved. increased ventilation. MH is fatal if left untreated.

In the past few years, I have been contacted to review the There are other cases of genetic mutations in breeds of
medical records, anesthesia record, and postoperative dogs responsible for adverse or toxic responses to medi-
records on Chows who have died during the immediate cations normally used in dogs without these adverse
postoperative / post anesthetic period following routine, effects in most dog breeds.
not emergency surgery in a young otherwise healthy
Chow Chows. In one recent case, I also performed the The best described is the potentially fatal neurotoxicity
necropsy and histopathologic review. In my 26 years as a in Collie lineage dogs following ivermectin use in the
veterinarian, many other of my own and client’s Chows 1980s as a parasiticide3. Ivermectin targets a chloride ion
have had routine sedation, anesthesia surgery without channel in invertebrates such as nematode (D. immitis)
incident. However, the rectal temperature is checked be- responsible for heart worm disease and arthropods such
fore, during, and frequently in the post-operative period as lice and mites. Ivermectin is generally safe in domestic
when my patients are closely monitored during recovery. animals because this channel in mammals is restricted
to the central nervous system and protected by the blood
It is unclear if there is genetic a problem in the Chow as brain barrier. The multiple drug resistance gene (MDR1)
breed responsible for the increase risk of post anesthesia is responsible for P-glycoprotein which is essential for
/ surgery complications / death following routine surgery the blood brain barrier function and mammals with a
or factors such as poor postoperative monitoring. Below specific genetic mutation (MDR1-1Ä) are have an ex-
is a brief review of some of the genes known to cause tremely toxic reaction to ivermectin and some anticancer
problems related to specific drugs in dogs. drugs. In 1994, mice lacking a specific gene, adenosine
triphosphate (ATP)-binding cassette subfamily B, mem-
The genetic basis for the most common type of malig- ber 1 (Abcb1a) had the same observed findings (pheno-
nant hyperthermia (MHS1) is due to mutations in the type4) as observed in dogs with MDR1-1Ä mutations.
gene for the type 1 ryanodine receptor (RYR1), a calcium The mouse Abcb1a gene is an ortholog5 to the human
release channel in skeletal muscle cells. Over 200 muta- MDR1 gene. The canine MDR1-1Ä gene mutation was
tions in RYR1 gene associated with MHS1 in humans subsequently changed to ABCB1-1Ä.
have been identified1.
There is ongoing research into potential gene mutations
Reports from 2007, MH is considered hypermetabolic interfering with or prolonging drug metabolism in the
response to potent inhalation anesthetic gases such as Chow at the Washington State University, Pullman, WA.
halothane, sevoflurane, desflurane, and the muscle relax- Research with rough coated-collies where those with the
ant, succinylcholine, and uncommonly in humans sec- ABCB1-1Ä mutation show both an increased depth and
ondary to vigorous exercise and heat2. Further, clinically duration of acepromazine sedation6. There are anecdotal
MH may occur at any time during anesthesia and in the reports of prolonged or excessive sedation with some
early postoperative period. The earliest signs are tachy- opiates in dogs with the ABCB1-1Ä mutation as well as
cardia, rise in end-expired carbon dioxide concentra- other breed specific considerations for anesthesia includ-
tion despite increased minute ventilation, accompanied ing brachycephalic breeds of dogs7.
by muscle rigidity, especially following succinylcholine
administration. Chow Chows are considered a brachycephalic breed due
to their shortened muzzle length in comparison to their
Body temperature elevation is a dramatic, but head. However, brachycephalic dogs (Pugs, Bulldogs,
often late sign of MH. A MH response may not etc.) with additional serious structural problems (elon-
occur with the first or even second time a drug is gated soft palate, stenotic nares, hypoplastic trachea, or
given, it can sometimes take three times before everted laryngeal saccules) can have also have problems
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